The invention relates to new liquid-crystal guest-host systems having at least two pleochroic dyestuffs.
Although numerous publications have dealt with liquid-crystal guest-host systems (G. H. Heilmeier and L. A. Zanoni, Appl. Phys. Lett. 13, 91 (1968); D. L. White and G. N. Taylor, J. Appl. Phys. 45, 4718 (1974); T. Uchida, H. Seki, C. Shishido and M. Wada, Mol. Cryst. Liq. Cryst. 54, 161 (1979)), they have not hitherto found any commercial use. In essence, there are two reasons for this: in the first place, a guest-host mixture which remained achromatic with respect to disparate modes of illumination and at the same time, in particular, with differing layer thicknesses of the guest-host system in the electro-optical display element has not existed. In addition, to date, the guest-host systems have only been suitable for a restricted temperature range (indoor use), since they have exhibited a markedly higher viscosity than the host material.
However, nowadays there is an increasing demand for a very wide temperature range (outdoor use), which is conditional on having guest-host systems which can still be operated even at very low temperatures.